1. Field of the Invention
This invention relates generally to flat panel display devices, and more particularly, to large flat panel display devices that use one or more support structures for internally spacing the faceplate and the backplate, with the support structures providing for charge bleed off.
2. Description of the Related Art
In recent years there have been numerous activities relating to the construction of flat panel displays to replace conventional deflected-beam CRT displays. Flat panel displays are lighter and less bulky. In addition to flat CRT displays, other flat panel displays, such as plasma displays, have also been developed.
Flat panel displays include a faceplate, a backplate and connecting walls around the periphery of the faceplate and backplate, forming a vacuum envelope. In some flat panel displays, the envelope is held at vacuum pressure which in the case of CRT displays the vacuum held is about 1.times.10.sup.-7 torr or less. The interior surface of the faceplate is coated with light emissive elements, such as phosphor or phosphor patterns, which define the active region of the display. Cathodes located adjacent to the backplate are excited to release electrons which are accelerated toward the phosphor on the faceplate. The electrons impact the phosphors, and the phosphors emit light seen by the viewer at the exterior of the faceplate.
The vacuum environment produces a force which is exerted on the walls on the flat panel display. If left unopposed, the flat panel display can collapse. In rectangular displays having greater than approximately a 1 inch diagonal, the faceplate and backplate are particularly susceptible to this type of mechanical failure due to their high aspect ratio. The aspect ratio is the distance between support structure in the display divided by the thickness of the faceplate or backplate. The faceplate or backplate of a flat panel display may also fail due to external forces resulting from impacts sustained by the flat panel display.
Spacers have been used to internally support the faceplate and/or the backplate. Previous spacers have been walls or posts located between pixels (phosphor regions that define the smallest individual picture element of the display) in the active region of the display.
Spacers can adversely affect the flow of electrons toward the faceplate in the vicinity of the spacer. Stray electrons may electrostatically charge the surface of the spacer, changing the voltage distribution near the spacer from the desired distribution and resulting in distortion of the electron flow. This results in distortions in the image produced by the display.
The use of spacer walls has been reported in U.S. Pat. No. 4,900,981; U.S. Pat. No. 5,170,100; EPO 464 938 A1; EPO 436 997A1 where horizontal walls in the display are used to localize electron beam withdrawals through apertures; EPO 580 244A1 where the wall structures have a very high ohmic layer on only the fine selection side of the walls; and EPO 496 450 A1 which discloses wall structures made of a variety of materials.
It would be desirable to provide a flat panel display device with spacers that have a low enough sheet resistance to bleed charge. There is a need to bleed charge away from the spacer, e.g., stray electrons from the electron source striking spacers, and yet maintain the high potential difference across the spacer without running a high current through it, and also permit the tailoring of potential distribution.